Immersion Heater in 1.5mm flex

GEOFF S · Jan 28, 2016

Amp David said:
Which reg relates to 'pushing it'?

Hi

No reg relates to pushing it, i personally dont like running cables near to their maximum, some heat resistant cables have a ccc less than 16 amps some more, also i like to derate due to ambient temp. So 2.5mm runs cooler, less volt drop, better thermal constaints etc. I never said 1.5mm couldnt be used, it depends upon the cable and other factors.

You all have your preferences and veiws, some a little emphatic, i have mine.

Cheers

davesparks · Jan 28, 2016

GEOFF S said:
Hi

No reg relates to pushing it, i personally dont like running cables near to their maximum, some heat resistant cables have a ccc less than 16 amps some more, also i like to derate due to ambient temp. So 2.5mm runs cooler, less volt drop, better thermal constaints etc. I never said 1.5mm couldnt be used, it depends upon the cable and other factors.

You all have your preferences and veiws, some a little emphatic, i have mine.

Cheers

The tabulated values in the regs book are not the maximum for the cables, they are already worked out to avoid running the cables at their maximum!
All you do by applying the 'I don't like running near the max' approach is to end up wasting money.
Plus the ratings are already at 30degrees so to apply a factor for normal room temperature in this country would actually increase the ccc.

Plus of course the terminals on an immersion heater and cable grip are designed for 1.5 so using bigger cable often leads to broken cable clamps and poor terminations

GEOFF S · Jan 28, 2016

davesparks said:
The tabulated values in the regs book are not the maximum for the cables, they are already worked out to avoid running the cables at their maximum!

All you do by applying the 'I don't like running near the max' approach is to end up wasting money.
Plus the ratings are already at 30degrees so to apply a factor for normal room temperature in this country would actually increase the ccc.

Plus of course the terminals on an immersion heater and cable grip are designed for 1.5 so using bigger cable often leads to broken cable clamps and poor terminations

Hi

Which tabulated values are they dave? i think you will find they are max values, reference a table please.

Well Dave the life span of a cable reduces the higher the temp, waste money, i dont think so, i bet the I2R losses would easily pay for the bigger cable.

Those little cupboards get toasty with a big copper radiator an ambient temp of 35 C is prudent dont you think?

Your clearly using inferior elements, go for quality.

Cheers

Midwest · Jan 29, 2016

GEOFF S said:
Hi

Which tabulated values are they dave? i think you will find they are max values, reference a table please.

Well Dave the life span of a cable reduces the higher the temp, waste money, i dont think so, i bet the I2R losses would easily pay for the bigger cable.

Those little cupboards get toasty with a big copper radiator an ambient temp of 35 C is prudent dont you think?

Your clearly using inferior elements, go for quality.

Cheers

Looking at table 4F3A, which states current-carrying capacity (no mention of minimum or maximum). I note the current carrying capacity of flexible cables (single phase & non armoured) for 1.5mm & 2.5mm to be 16amp & 25amp respectively. The table does not submit an ambient temperature for those particular figures. However, does start to give rating factors for ambient temperatures from 35'c.

It also provides rating factors for 110'c, 150'c flexible cables, 35-80'c x 1 & 35-120'c x 1 respectively, i.e. no effect on current carrying capacities for those cables at those temperature ranges.

If we are to assume the ambient temperature of an immersion heater cupboard to be 40'c (i'e just measured mine at 33'c), a rating factor of 0.82 would apply.

Therefore, a standard flexible cable of 1.5mm & 2.5mm, would have capacity of 13.12a & 20.5a. Heat resistant flexible cables would not have their capacities, affected by this particular ambient temperature.

I see that some heat resistance flexes are sold as heat resistance to 85-90'c range.

My observations are; standard flexible cables would be at or above their limit, in terms of their current carrying capacities in the above scenario, whereas heat resistance would not. To use 2.5mm heat resistance flex for 3kw immersion heater, is not necessary whereas 1.5mm is more than sufficient.

GEOFF S · Jan 29, 2016

Midwest said:
Looking at table 4F3A, which states current-carrying capacity (no mention of minimum or maximum). I note the current carrying capacity of flexible cables (single phase & non armoured) for 1.5mm & 2.5mm to be 16amp & 25amp respectively. The table does not submit an ambient temperature for those particular figures. However, does start to give rating factors for ambient temperatures from 35'c.

It also provides rating factors for 110'c, 150'c flexible cables, 35-80'c x 1 & 35-120'c x 1 respectively, i.e. no effect on current carrying capacities for those cables at those temperature ranges.

If we are to assume the ambient temperature of an immersion heater cupboard to be 40'c (i'e just measured mine at 33'c), a rating factor of 0.82 would apply.

Therefore, a standard flexible cable of 1.5mm & 2.5mm, would have capacity of 13.12a & 20.5a. Heat resistant flexible cables would not have their capacities, affected by this particular ambient temperature.

I see that some heat resistance flexes are sold as heat resistance to 85-90'c range.

My observations are; standard flexible cables would be at or above their limit, in terms of their current carrying capacities in the above scenario, whereas heat resistance would not. To use 2.5mm heat resistance flex for 3kw immersion heater, is not necessary whereas 1.5mm is more than sufficient.

Hi

I find this a strange remark, 1.5mm is a minimum and with some cables inadequate. Unnecessary means excessive, so what is excessive about installing 2.5mm cable, the cost, crikey?

Ill give you some pro's, you give the con's

Lower operating Temp
Less Volt Drop
Lower I2R
Can be used as a supplemetary bonding conductor
A longer life span
More Robust
Pretty much all flexible cables even derated will be okay.

Cheers

Midwest · Jan 29, 2016

GEOFF S said:
Hi

I find this a strange remark, 1.5mm is a minimum and with some cables inadequate. Unnecessary means excessive, so what is excessive about installing 2.5mm cable, the cost, crikey?

Ill give you some pro's, you give the con's

Lower operating Temp
Less Volt Drop
Lower I2R
Can be used as a supplemetary bonding conductor
A longer life span
More Robust
Pretty much all flexible cables even derated will be okay.

Cheers

Sorry didn't want my reply to say strange.

I was just suggesting that, in my example the 1.5mm flex was suitable for the designed load. 2.5mm is also suitable, but as you eluded to, slightly more expensive. The bigger flex is slightly more difficult to install, but not totally impracticable. I guess the reason I would use, is that the smaller cable is suitable & more cost effective, and however small that might be (approximately 80p per metre?), that can be passed onto the customer.

As to pros & cons, I'm not sure, over the length of cable normally used for connections to immersion heaters, whether your pros would have a huge impact on selection, but I'm willing to be convinced otherwise. Perhaps you could expand.